Tuesday 9 January 2024


When it comes to Antenna Tuning Units, I have the wonderful little Elecraft T1 and the LDG Z-100PLUS. They are both 'automatic' tuners - there is no manual tuning facility - you simply transmit some RF and the units will automatically search for the best match between your antenna and transmitter.

But what if you are using a receiver and can't transmit? Well you're stuck with your mismatch and as a result, your signal may be considerably weaker than it might otherwise be. This is when you would benefit from a manual ATU with knobs and dials. Of course you could use a simple Coupler but then you are limiting yourself to an RX-Only device.

The answer is to find a manual ATU and there are plenty of them available, but I was eager to find a small one! My first choice would have been an EMTECH ZM-2 but they are ridiculously expensive here in the UK due to the exorbitant shipping costs and the Customs & Excise Duties.

The answer was found right here in England at Kanga Products. They sell a 'Pocket Transmatch' which is small, easy to use and is able to work with both a Transceiver and a Receiver. It is available as a pre-built unit or as a self-build kit (with around 50 components). I chose the latter for £45. It's only a tenner more to have it pre-assembled, which is a bargain, but where's the fun in that? 😂

The kit provides you with everything you need including a rather nice case with printed panels. It measures just 85mm x 55mm and weighs just over 100g. It comes with BNC connectors, covers 80-10M and can handle up to 10W - perfect!!

As its name suggests, this is more than a regular ATU - it's a Transmatch which benefits from introducing some bandpass filtering and is  much better than traditional L-Match circuits. The design is made up of two circuits, the first one being a Resistive SWR Bridge and the second part of the circuit is the actual ATU. This device has a switch to permit the use of Balanced and Unbalanced feeds.

This kit comes with fabulous build-instructions but Kanga warn that this is the most difficult kit in their range and I'm guessing they say that because of the toroid which needs winding. A couple of years ago I would have been a little anxious about tackling this, but really, it's a very, very easy process (if a little fiddly). 

Winding toroids (especially ones with multiple windings and loops) can be quite daunting to newcomers, but believe me, there's nothing magical or mystical about the process - it's just a case of paying attention to the number of turns and making sure that you're being neat.  Taking a photo using your mobile phone and then zooming in to count the turns (and examine for any overlapping) can make the process much easier.

After I built a QRPLABS QDX, I never worried again about winding toroids, so rather than repeat myself here, I suggest that you read through the relevant section of that build for some guidance.

The toroid supplied in this kit is a T68-2 Core and it's not a bad size - meaning that the windings aren't so tight that it'll make your life hell. You basically wind 13 turns, create a short loop, do another 6 turns, create a second loop and then finish off with another 13 turns. That leaves plenty of room on the core.

Next up is to use a separate piece of wire to wind on 7 turns between the existing winding starting 3 turns in. This second piece of wire is coloured differently to make it easy to see what you're doing. The photo below might explain what I mean.  Again, this will probably look quite daunting to a newcomer, but honestly, it's quite easy to do and you can always check it again by zooming into a photo of it on your mobile phone.

Once you have the toroid in place, the rest is pretty darn simple - just a case of soldering a few through-hole components. As per the instructions, do not solder the red LED yet.  It's important to note that when you fit the two toggle-switches to the PCB, you should not press them all the way down to the PCB - just push the terminals through enough so that you can solder them. If you push them too far down into the PCB, you might not have enough thread sticking through the enclosure's faceplate to fit the retaining nut (although that's only really decorative). Also make doubly sure that the switch is perfectly straight before soldering.

You do have to exercise a little caution when preparing the two variable capacitors because it involves cutting off some of the legs, but if you pause to double-check the instructions, it's a simple process.

Once you've fitted the caps to the front panel and secured with screws, attach some of the insulation tape provided to the back of the caps. This is to prevent anything on the PCB touching the caps. Once that's done, you simply lower the PCB onto the legs of the capacitors. Note that as you are lowering the PCB down, you need to guide the LED into its panel aperture. When you're happy with everything, solder the caps and LED.

The final part is to fit the BNC connectors using the shortest amount of wire that you can manage to work with. Insert the supplied spacer and secure the front panel with the 4 screws. Job done!!

I tested the Pocket Transmatch using an EFHW antenna with my tiny 5W (tr)uSDX transceiver and everything worked perfectly. I might open it back up and adjust the blue sensitivity-trimmer so that the LED goes out completely when the perfect match is found, instead of going very dim.

Size-wise, the ATU is a perfect match for the (tr)uSDX  (in fact it's smaller than the radio) and it can easily handle the power (which can sometimes creep up to 7 or 8W depending on the band and the input voltage).

As for operating the ATU, it couldn't be simpler. You flick the toggle from OPER to TUNE, transmit a constant carrier and then turn the dials until the LED goes out (or goes really dim). I tried it numerous times and the dimmest level of the LED matched the best SWR reading on the radio. Perfect!  When you've found your match, flick the toggle switch back to OPER and away you go.

Next up was to try it with a receiver, so I connected it to my AOR AR-DV1 and (to give it a hard time) my G5RV antenna. I started with both tuning dials to the far left (anti-clockwise) position - I believe that position is close to a 'straight-thru' or 'bypass'.  I then tuned into a signal and adjusted the left dial until I heard the most noise and then turned the right dial for the same. Repeating this exercise a couple of times got me the best possible signal and a massive improvement on what I would have otherwise heard.

So this little device is a very worthwhile addition to the shack and I'm really pleased with it. It's tough, compact and can handle all the power I need out in the field. At 80-10M it also has good band coverage. With the enjoyment of kit-building, it's also worth every penny of the £45.

Great job, Kanga!

73, Tom, M7MCQ.

UPDATE : A few days after posting this, I was contacted by someone who had built the DeskTop version. He wasn't using it and offered to sell it to me. It cost me £22 plus postage. Love a bargain!!


Alan said...

Hi Tom
I got the Kanga MTM-ATU the desktop version which is very similar and small enough to take out in the field for use with my QCX-mini. It works great.
All the best for 2024, 73
Alan G4KRN

VE9KK said...

Good afternoon Tom, very nice job putting the tuner together and excellent job on the toroids! I can remember the first few times I tackled a toroid and as you say it can cause some stress. But as you say once you get the hang of it no problem after that.
Thanks for another great review!

MadDogMcQ said...

@ALAN : Thanks for the visit Alan! I didn’t realise the ‘desktop’ version was so small until after I ordered the Pocket version, lol. No matter - they’re obviously both great items. All the best to you and yours. 73, Tom, M7MCQ.

@MIKE : Thank you for the kind words Mike. I hope you and yours are in good health and enjoying the new year. Best wishes, Tom, M7MCQ.